Following messy divorces, many ex-spouses will go to great lengths to get revenge -- some will have even try to wreak havoc on your reputation by contacting the IRS.

John Lieberman, a CPA at Perelson Weiner LLP, said he has heard of people telling the IRS that their ex-spouse laundered money, committed serious financial crimes, underreported income, even owned a brothel.

"[Ex]-spouses love writing letters to the IRS," said Lieberman.

It's not just the ex-wife or husband you have to watch out for. Lieberman said he worked on one case where the mother-in-law told the IRS that her ex-son-in-law was a money launderer.

Sometimes the claims are completely made up, while others are legitimate. And while some people write in anonymously, others divulge their names -- which is required in order to claim a whistleblower reward of 15% to 30% of any extra money collected as a result of their tip.

NEXT: Your return has too many zeroes